Polishing technique to minimize abrasive removal of material and composition therefor

ABSTRACT

The present invention provides a composition and a method of polishing a surface that minimizes abrasive removal of material from the surface. To that end, the composition is formulated to maximize dissolution of the material from the surface.

BACKGROUND OF THE INVENTION

The field of invention relates generally to the fabrication of integrated circuits. More particularly, the invention relates to compositions and methods for using polishing layers of material in furtherance of fabricating semiconductor circuits.

The fabrication of modern semiconductor devices includes forming multiple layers of conductive and dielectric materials on substrates. To that end two various processes are employed to deposit and to remove material associated with the layer. Exemplary deposition techniques include electrochemical deposition, chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), atomic layer deposition (ALD), physical vapor deposition (PVD) and the like. Exemplary removal techniques include etching, such as chemical or plasma etching, as well as polishing.

Chemical-mechanical polishing (CMP) methods and polishing slurries are well known and widely used techniques for polishing layers to provide the same with a smooth, if not planar, shape. Often, however, the surface being polished has regions with differing materials present, e.g., materials with differing mechanical properties and chemical reactivity. As a result, the removal rate over the surface is not uniform, which makes obtaining the desired planarization of the surface difficult, while minimizing roughness over the area thereof. For example when polishing a surface having a metal region surrounded by dielectric, minimization of dishing is difficult. Dishing results from one of the regions, e.g., the metal region, being removed at a greater rate than the rate at which the other regions of the surface are removed. This results in a concave region in the metal area, which is often undesirable when a planar shape is desired. To avoid the deleterious effects of CMP of surfaces having regions of differing material properties, various CMP slurries have been developed to obtain desirable CMP characteristics: low polish induced damage, high polishing rate, process predictability, high polished surface uniformity, low polished surface roughness, and the use of non-hazardous, low-cost polish materials.

Historically, polishing slurries for use in CMP contain fine, suspended abrasive particles to facilitate mechanical polishing of the surface, as well as acidic or basic chemical components to facilitate chemical polishing of the surface. The rate at which polishing occurs for a given material and operating conditions is related to the quantity of abrasive particles in the slurry. However, the damage to the surface being polished is also related to the size of the particles in the slurry. Chemical component selection may also dramatically affect polish rate and quality for a given material and operating conditions.

Additionally, advanced integration schemes, e.g., stacks with ultra low dielectric (ULK) and air gap integration schemes, are often structurally compromised by CMP processes through interfacial stress created during the CMP process, erosion, as well as absorption of CMP slurry chemicals.

Therefore, a need exists to provide improved techniques for polishing layers in furtherance of producing semiconductor circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a chemical-mechanical polishing machine known in the art but which can be used in practicing the present invention;

FIG. 2 is a schematic cross-sectional view of a chemical-mechanical polishing machine known in the art but which can be used in practicing the present invention;

FIG. 3 is a cross-sectional view showing an exemplary structure to undergo polishing in accordance with the present invention;

FIG. 4 is a cross-sectional view showing a slurry composition in accordance with the present invention, being disposed between the exemplary structure of FIG. 3 and a polishing pad of the polishing machine shown in FIG. 1 in accordance with the present invention;

FIG. 5 is a cross-sectional view showing the exemplary structure of FIG. 3 having a surface undergoing polishing;

FIG. 6 is a cross-sectional view showing the exemplary structure of FIG. 3 after polishing in accordance with the present invention; and

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2, a brief overview of a polishing machine 10 is depicted that may be employed in accordance with the present invention. Polishing machine 10 has a platen 12, a wafer carrier 14, a polishing pad 16, and a slurry 18 on polishing pad 16. An under-pad 20 is typically attached to the upper surface 22 of platen 12, and polishing pad 16 is positioned on under-pad 20. A drive assembly 24 rotates platen 12 as indicated by arrow A. In addition, drive assembly 24 may cause platen 12 to reciprocate as indicated by arrow B. The motion of platen 12 is imparted to polishing pad 16 through under-pad 20 because polishing pad 16 frictionally engages under-pad 20. Wafer carrier 14 has a lower surface 26 to which a wafer 28 may be attached, or wafer 28 may be attached to a resilient pad 30 positioned between wafer 28 and lower surface 26.

Wafer carrier 14 may be a weighted, free-floating wafer carrier, or an actuator assembly 32 may be attached to wafer carrier 14 to impart axial and rotational motion, as indicated by arrows C and D, respectively. Polishing pad 16 may be embodied as a conventional polishing pad, a web-type polishing pad, a belt-type polishing pad, or any other polishing pad format known in the art. Polishing pad 16 may also be employed as a fixed-abrasive polishing pad. Such a fixed-abrasive polishing pad 16 may be impregnated with particulate abrasives including, but not limited to, alumina, titanium dioxide, silicon dioxide, and cerium dioxide. The abrasives in a fixed-abrasive polishing pad 16 are typically leached therefrom during polishing of wafer 28.

Referring to FIGS. 1 and 3, an exemplary wafer 28 that undergoes polishing in accordance with the present invention includes a substrate 40 having a recess 42 disposed within a surface 44. In a preferred embodiment, substrate 40 includes a dielectric layer and recess 42 is formed within the dielectric layer. A metal layer 48, such as copper, is disposed on surface 44 and substantially fills recess 42. A liner 50 is disposed between substrate 40 and metal layer 48, and is located on surface 44 and surfaces 46 of recess 42. Wafer 28 may comprise various other layers adjacent to recess 42, surface 44, liner 50, and/or metal layer 48, but for the purposes of simplicity of discussion, no other such structures are depicted.

Referring to FIGS. 4 and 5, to polish metal layer 48 in accordance with the present invention, slurry 18 is disposed between metal layer 48 and polishing pad 16. Polishing pad 16 is placed in close proximity to metal layer 48. Subsequently, polishing pad 16 is brought in frictional contact with metal layer 48 and, in combination with slurry 18, removes portions of metal layer 48. To attenuate, if not prevent, “dishing,” portions 52 of metal layer 48 are removed before portions 54 of metal layer 48, which are more distant from polishing pad 16. Once metal layer 48 is substantially removed outside the trench region, liner 50 is subsequently removed from surface 44 outside the trench region by continued polishing with slurry 18 and polishing pad 16.

Referring to FIG. 6, upon removal of metal layer 48 and liner 50 from outside the trench region, a new surface 144 is defined having first and second regions 146 and 148. First region 146 is comprised of metal from the remaining portions of metal layer 48, with second region 148 comprising substrate 40 and liner 50. As a result, surface 144 has varying material properties across an area thereof, with region 146 typically being harder than region 148, e.g. when region 148 is a dielectric material. As a result, were polishing pad 16 to impart a uniform force against surface 144 for a given slurry composition, the polish rate of region 146 may be greater than the polish rate of region 148. This may present as “dishing” in which region 146 has a concave shape.

The present invention, however, significantly attenuates dishing by changing the rate limiting step of the polishing operation. In the present invention, metal removal is controlled more by dissolution rather than kinetics during polishing of metal layer 48. Specifically, it was recognized that by controlling or limiting the removal rate by dissolution from surface 144, dishing may be avoided while at the same time minimizing roughness. For purposes of understanding the present invention, the polishing operation can be understood to have two principle operating mechanisms or steps, dissolution and kinetics. The kinetic step of removal can be defined as the reaction to form soluble metal oxides, while dissolution can be defined as the removal of the metal oxide by dissolving the same in a solvent. In the context of polishing copper, copper itself does not dissolve in solvents but copper oxide does. Thus, to effectively remove copper using solvent containing slurries, one has to first react the copper to form copper oxide. In the present invention, the removal process is principally governed or controlled by the removal of the oxides from the surface by dissolution, and not by kinetics at the metal interface.

Kinetic removal of material from surface 144 in accordance with the invention has less of an influence in the polishing rate in large part as a result of providing a neutral pH environment. In a preferred embodiment, this is accomplished using a reactive liquid (RL) slurry having a neutral pH. RL slurries are generally characterized by containing little or no abrasives, i.e., particles. Removal of materials is achieved primarily through chemical reaction of the material being polished with the RL slurry components.

More specifically, a composition in accordance with an embodiment of the present invention is provided with a pH that is generally in the range of 5 to 8. Optimal results were achieved using a pH of approximately 7.5. If present at all, particles in the slurry are generally no greater than 250 parts per million of the slurry composition or 0.0025 weight percent. Also included in the composition is a corrosion inhibitor that further minimizes kinetic removal of material from surface 144 during polishing. Other components of the composition may include an oxidizing agent, as well as a complexing agent that controls the rate of dissolution of the material from surface 144. An exemplary material from which region 146 is formed is copper. As a result, it is desired that the RL composition facilitate removal of copper. An exemplary corrosion inhibitor for the slurry composition may be a triazole-based compound, such as 1,2,4-triazole, C₂H₃N₃, and benzotriazole. Other suitable inhibitors may include imidazole, polyvinylimidazole, theophiline, bipyridyl, mercapto benzothizole,phenyl marcapto tetrazole, or pyrazole compounds. An exemplary oxidizing agent may be hydrogen peroxide, H₂O₂. An exemplary complexing agent may be dibasic ammonium citrate, (NH₄)₂HC₆H₅O₇, or more generally ammonium salts of citric, oxalic, tartaric, succinic, or actetic acids.

A first embodiment of the present invention may be as follows: COMPOSIITON 1 hydrogen peroxide dibasic ammonium citrate 1,2,4-triazole water Hydrogen peroxide consists of approximately 0.1% to 3%, and more preferably 1% to 3%, by weight of COMPOSITION 1, and dibasic ammonium citrate consists of approximately 0.1% to 12% by weight of COMPOSITION 1. 1,2,4-Triazole consists of approximately 1% to 6% by weight of COMPOSITION 1, with the remaining portion of the COMPOSITION 1 consisting of a carrier including water.

A second embodiment of the present invention may be as follows: COMPOSITION 2 hydrogen peroxide dibasic ammonium citrate benzotriazole water Hydrogen peroxide consists of approximately 0.1% to 3%, and more preferably 1% to 3%, by weight of COMPOSITION 2, and dibasic ammonium citrate consists of approximately 0.1% to 12% by weight of COMPOSITION 2. Benzotriazole consists of approximately 0.0001% to 3% by weight of COMPOSITION 2, with the remaining portion of COMPOSITION 2 consisting of a carrier including water.

A neutral pH RL slurry of the present invention offers many advantages over conventional slurries, including improved planarity. Specifically, copper is passivated when exposed to neutral pH compositions. It is believed that the passivation of copper during polishing provides improved planarization. Additionally, the neutral pH slurry of the present invention reduces the corrosion of the copper during polishing, thereby minimizing the formation of micro-trenches and minimizing roughness. As a result, the present neutral pH RL slurry provides wider process windows, lower defects, and ease of integration into present copper low-K dielectric layers.

The embodiments of the present invention described above are exemplary. Many changes and modifications may be made to the disclosure recited above, while remaining within the scope of the invention. For example, the components of COMPOSITIONS 1 and 2 are selected to facilitate planarization of surfaces having copper-containing materials and dielectric-containing materials. However, other components may be employed dependent upon the materials contained in the layer being polished. Therefore, this invention is not limited to the particular forms illustrated above. Nor is the invention limited or restricted to the particular theories, advantages, or perceived properties disclosed above. Rather, the invention should be defined as set forth in the appended claims and will cover all modifications that do not depart from the scope of this invention. 

1. A composition comprising: a carrier solution; a complexing agent to dissolve a predetermined material; and a corrosion inhibitor to minimize kinetic removal of said predetermined material, wherein said carrier solution, said complexing agent and said corrosion inhibitor being present in sufficient quantities to provide said composition with a neutral pH; and wherein said composition has a particle content no greater than approximately two hundred and fifty parts per million.
 2. The composition as recited in claim 1, wherein said neutral pH is in a range of 5 to
 8. 3. The composition as recited in claim 1, wherein said carrier solution further includes hydrogen peroxide.
 4. The composition as recited in claim 1, wherein said complexing agent comprises ammonium salts of citric, oxalic, tartaric, succinic, or actetic acids.
 5. The composition as recited in claim 4 wherein said complexing agent comprises dibasic ammonium citrate.
 6. The composition as recited in claim 1, wherein said corrosion inhibitor comprises triazole.
 7. The composition as recited in claim 1, further comprising an oxidizing agent, wherein said oxidizing agent includes approximately 0.1% to 3% by weight of said composition of hydrogen peroxide.
 8. The composition as recited in claim 1, wherein said complexing agent includes approximately 0.1% to 12% by weight of said composition of dibasic ammonium citrate.
 9. The composition as recited in claim 1, wherein said corrosion inhibitor includes approximately 1% to 6% by weight of said composition of an inhibitor selected from the group consisting of triazole, imidazole, polyvinylimidazole, theophiline, bipyridyl, mercapto benzothizole,phenyl marcapto tetrazole, and pyrazole.
 10. The composition as recited in claim 1, wherein said corrosion inhibitor includes benzotriazole.
 11. The composition as recited in claim 1, wherein said corrosion inhibitor includes 0.0001% to 1% by weight of the composition of benzotriazole.
 12. A composition comprising: a carrier solution including hydrogen peroxide; a complexing agent; and a corrosion inhibitor, wherein said carrier solution, said complexing agent and said corrosion inhibitor are present in sufficient quantities to provide said composition with a neutral pH, with a range of particles contained therein in a range of zero to 250 parts per million.
 13. The composition as recited in claim 12, wherein said complexing agent comprises dibasic ammonium citrate.
 14. The composition as recited in claim 13, wherein said corrosion inhibitor includes benzotriazole.
 15. The composition as recited in claim 13, wherein said corrosion inhibitor comprises triazole.
 16. The composition as recited in claim 12, wherein said hydrogen peroxide is present in said composition in a quantity of approximately 1% to 3% by weight.
 17. The composition as recited in claim 16, wherein said complexing agent includes approximately 0.1% to 12% by weight of said composition of dibasic ammonium citrate.
 18. The composition as recited in claim 17, wherein said corrosion inhibitor includes approximately 1% to 6% by weight of said composition of triazole.
 19. The composition as recited in claim 17, wherein said corrosion inhibitor includes 1% to 3% by weight of the composition of benzotriazole.
 20. A method for polishing a layer containing conductive material and dielectric material, said method comprising: removing portions of said layer by exposing said layer to a composition at a rate of removal, with said rate of removal being principally controlled by a dissolution of said layer with said composition, wherein said composition includes a quantity of particles in a range of zero to two hundred fifty parts per million.
 21. The method as recited in claim 20, wherein said composition has a neutral pH and kinetics of oxide formation do not control removal rate.
 22. The method as recited in claim 20, wherein said composition has a pH in a range of 5-8.
 23. The method as recited in claim 20, wherein said composition has a pH of approximately 7.5.
 24. A method for polishing a layer having conductive material and dielectric material, said method comprising: removing portions of said layer using a composition to generate a substantially smooth surface including first and second regions, with said first region including said conductive material and said second region including said dielectric material, wherein kinetics of conductive oxide formation do not principally control the removal of material from one of said first and second regions.
 25. The method as recited in claim 24, wherein removing further includes principally controlling removal rate by dissolution with the composition.
 26. The method as recited in claim 24, wherein said composition has a pH in a range of 5-8.
 27. The method as recited in claim 26, wherein said composition has a pH of approximately 7.5.
 28. A method for making a semiconductor device comprising: providing a slurry composition having a particle content no greater than approximately two hundred and fifty parts per million and comprising: a carrier solution; a complexing agent to dissolve a predetermined material; and a corrosion inhibitor to minimize kinetic removal of said predetermined material, wherein said carrier solution, said complexing agent and said corrosion inhibitor being present in sufficient quantities to provide said composition with a neutral pH; providing a semiconductor substrate having a trench formed within a dielectric layer, the trench having a metal layer therein; providing a polishing apparatus having a polishing pad; polishing a surface of the semiconductor substrate using the polishing pad and the slurry composition.
 29. The method as recited in claim 28 wherein wherein said neutral pH is in a range of 5 to
 8. 30. The method as recited in claim 28 wherein said carrier solution comprises hydrogen peroxide.
 31. The method as recited in claim 28 wherein said complexing agent comprises dibasic ammonium citrate.
 32. The method as recited in claim 28 wherein said corrosion inhibitor comprises triazole.
 33. The method as recited in claim 28 wherein said corrosion inhibitor comprises benzotriazole. 